[VideoPlayer] Hide the spinner on playing the video

This patch fixes the regression by https://codereview.chromium.org/1134603002/diff/1/ui/file_manager/video_player/css/video_player.css

BUG=488213
TEST=none

Review URL: https://codereview.chromium.org/1141183004

Cr-Commit-Position: refs/heads/master@{#330342}

ui/file_manager/video_player/css/video_player.css

@@ -40,7 +40,7 @@ body {
 }
 
 #spinner-container {
-  display: block;
+  display: none;
   height: 100%;
   left: 0;
   position: absolute;